The transfer case off the 2.5L is likely 21spline, and the output for the D300 is likely 23spline. Otherwise the bolt pattern should be the same, and your 231 would work by swapping out the input shaft.
To remove the shifer for the AX5 (if that's your stock 2.5L tranny) you have to go further down torward the tranny and lift up the round rubber boot on the shift tower. Depress the spring-loaded locking ring under this boot and rotate it and it'll pop right out. Or remove the 4 bolts holding the shock tower on, turning the spring loaded collar is the easier of the two.